Seeing the damage (emotional) that I was doing to those around me. At the point I was at my health wasn't my concern. I could feel better with a couple shots of bourbon.
Then my DW whose opinion I treasure said to me "When you used to walk into a room people got exited like , HEY LOOK ALAN'S HERE. Now they are like OH GREAT ALAN"S HERE as they look for the exit" That was a nail in the coffin to see that my drinking was impacting others. Also quite a blow to my over-inflated ego. What it was, was a reality check. And I needed it..